ref: 0977f294bab0345ba43fbf674449fd8e996c5719
dir: /man/2/wait/
.TH WAIT 2
.SH NAME
wait \- wait for child process to exit
.SH SYNOPSIS
.EX
wait := load Wait Wait->PATH;
Wait: module
{
init: fn();
read: fn(fd: ref Sys->FD): (int, string, string);
monitor: fn(fd: ref Sys->FD): (int, chan of (int, string, string));
parse: fn(status: string): (int, string, string);
};
.EE
.SH DESCRIPTION
.B Wait
helps use the
.B wait
file of
.IR prog (3).
.PP
.B Init
must be called to initialise the module before invoking any other function.
.PP
.B Read
reads a single wait record from file descriptor
.IR fd ,
which must be open on some process
.IR p 's
.B wait
file,
and returns a tuple
.BI ( pid\f5,\fP\ module\f5,\fP\ status )
where
.I pid
is the process ID of a child of
.I p
that has exited,
.I module
is the name of the module that caused
.I p
to exit,
and
.I status
is nil if
.I pid
ended without error or a status message otherwise.
If reading the
.B wait
file resulted in end of file or error,
.I pid
is 0 (for end of file) or
.B -1
on error (and
.I status
is the system error string for the error).
.PP
.B Monitor
provides a channel interface to the
.B wait
file open on
.IR fd ;
it allows, for instance,
a process to use
.B alt
to exchange data with a process but also see it exit (for good or ill).
It starts a monitor process that applies
.B read
to
.I fd
and sends each resulting tuple on a channel.
It returns a tuple
.BI ( pid\f5,\fP\ c )
where
.I pid
is the process ID of the monitor process (which can be used to kill it when done with it),
and
.I c
is the channel on which the process sends each value it reads.
The tuple has the format described above for
.BR read .
The monitor process exits when the wait file
.I fd
yields end of file or error, after sending the corresponding tuple on
.IR c .
.PP
.B Parse
takes a complete
.I status
string as read from a
.B wait
file and returns a tuple
.BI ( pid\f5,\fP\ module\f5,\fP\ status )
as described for
.B read
above.
.SH SEE ALSO
.IR sh (1),
.IR prog (3)